The Section runs the Laboratory of Muscle Enzyme Histochemistry that processes up to 300 muscle and nerve biopsies per year for diagnostic studies. Examined muscle specimens are from patients with neuromuscular manifestations related to systemic autoimmune, viral, metabolic, endocrine or infectious diseases, and from patients with primary neuromuscular disorders, such as polymyositis, dermatomyositis, neurogenic muscular atrophies, muscular dystrophies, post-polio syndrome, polyneuropathies, mitochondrial encephalomyopathies and biochemical or genetic muscle diseases. The laboratory is also involved in the following immunologic, biochemical and virologic studies that examine the susceptibility of the muscle and nerve to immune or viral mediated injuries: (a) Study of the regeneration of human muscle in health and disease, and monitor the maturation of satellite cells by examining the expression of neural cell adhesion molecules and laminins; (b) study the susceptibility of muscle and nerve to infection with retroviruses and the ability of HIV or HIV-infected lymphoid cells to infect human myotubes in culture and induce expression of MHC-antigens; (c) study the expression of the poliovirus receptor in human muscle and the ability of the poliovirus to infect and replicate in human myotubes; (d) study the toxicity of AZT to muscle mitochondria by applying various concentrations of AZT to human muscle in culture; and (e) use of animal models to study the pathogenesis of: (i) retrovirus-induced inflammatory myopathy by examining muscles from monkeys infected with simian immunodeficiency virus; (ii) AZT-induced mitochondrial myopathy by studying structural, metabolic and functional changes in the muscle, heart, and brain mitochondria in rats injected with AZT; and (iii) autoimmune demyelinating polyneuropathies by searching for myelinotoxic or axonotoxic autoantibodies in sciatic nerves of rats after intraneural injection of the patient's serum.